This invention relates generally to ultrasonic scanning systems for use in observing organs in the body and more particularly to an ultrasonic sector scanning system.
In recent years ultrasonic scanning of regions of the human body has found wide applications. Among the advantages of such scanning systems is that the energy required is low, greatly reducing the possibility of injury to the patient; there are no side effects of radiation; and the body is not invaded.
The ultrasound is transmitted in a beam including brief pulses each followed by a relatively long interval where no transmission occurs. During this interval the pulse energy is transmitted through the body. Whenever a pulse of energy strikes a boundary between two substances having different acoustic impedances, a portion of the energy is reflected, some of it returning as an echo to the source. The remaining portion of the original energy is available to produce additional echoes from deeper interfaces. The crystal which serves as the transducer converting electrical energy into sound pulses receives the echoes and generates an electrical signal. This signal is amplified, displayed as a static or dynamic pattern on a cathode ray tube. The relative positions of the interfaces are shown on the display.
A particular type of scanner used is a sector scanner since it has the ability to display a cross-sectional area of the human body. A sector scanner generally comprises an ultrasonic transducer (a piezoelectric element) which is mounted and motor driven through a suitable mechanical arrangement. The drive arrangement moves the transducer which is generally in the form of a flat circular object back and forth in an arc scanning motion. During this process, the transducer is pulsed with high voltage spikes at pulsed repetition rates in the order of 3000 Hz. These spikes cause the piezoelectric element to mechanically ring, thereby emitting high frequency sound waves. These ultrasonic waves impinge upon the structure within the body and, when difference of acoustic impedance exists, are partially reflected back to the transducer element. At this point, the transducer element acts like a receiver and converts these mechanical vibrations to electrical energy. This energy is amplified and processed such that it can be displayed on a cathode ray tube.
The mechanical driving arrangement not only drives the probe but also provides an electrical output analogous to transducer position by the use of position sensing means such as a potentiometer which translates position information into electrical energy. The electrical signal is processed and utilized to create horizontal and vertical signals which, along with the returning ultrasonic impulses, are used to create an X-Y display on the cathode ray tube. The resultant image is a representation of the internal organs of the body.
In order for the information displayed on the cathode ray tube monitor to be most effective in use, it is necessary to record these images so that they can later be viewed and compared. The methods presently employed take the form of a movie camera photographing the monitor display or a television camera focused on the monitor connected to a video tape recorder. Electrostatic and similar printers have also been used.
Another prior art system which allows real time examination of internal organs of the body such as the heart employs a catheter which has a rotating tip which carries a plurality of transducers. The transducers are selectively connected to a pulser to transmit ultrasonic pulses into the body and to receive echoes therefrom. The echo pulses are processed and applied to a cathode ray tube whereby they provide sequential representations of the area at a rate which is dependent upon the speed of rotation of the transducers and with a resolution which is dependent upon the pulse rate. Field rates are selected so that the display can be photographed with a movie camera, for example, 24 frames per second. The system briefly described above is the subject of U.S. Pat. No. 3,779,234.
In all the prior methods there is no system approach. Each device, display and recorder, operate in their normal mode. There is no attempt to combine the characteristics and advantages of each to obtain a better result and reduce the overall cost of the system.